The present invention relates to compositions for staining biological tissue of the type comprising a cationic dye component, an anionic dye component, a stabilizer and an alcohol-containing solvent; and especially to such compositions of the Romanowsky type.
Romanowsky-type stains, and especially Wright stains, provided in an alcohol solution, are commonly used to stain biological tissue such as blood smears, malarial parasites and bone marrow. Unstabilized compositions are prone to reactions during storage that produce an undesired precipitate and loss of staining ability. A number of proposals have been made regarding the mechanism of this reaction and compositions have been prepared which are stabilized in various ways to counteract these problems. Some of the proposals have involved pH control (Gilliland et. al. Stain Technology Vol. 54, No. 3, pp. 141-150 (1979)), introduction of the anionic dye component (especially Eosin Y) in the free acid form rather than the alkali metal salt form (U.S. Pat. No. 4,392,864 to Helfrich et al (1983)) or addition of stabilizers (U.S. Pat. Nos. 4,290,769 (1981) and 4,382,075 (1983), each to Liao et al).
Among the stabilizers proposed have been ammonium halides and primary, secondary or tertiary alkylamine hydrohalides having alkyl chains of 1-6 carbons. Especially mentioned have been diethylamine hydrochloride and dimethylamine hydrochloride; both of which are secondary amines of petrochemical origin.